Many mobile machines, such as off-highway mining trucks, loaders, motor graders, material handlers and hydraulic excavators, include numerous moving parts that require proper lubrication to prevent premature failure. Critical areas may include, for example, wheel bearings, articulation joints and linkage joints. In many applications, these critical areas must be frequently lubricated, e.g. it may be desirable to lubricate as frequently as every 5-10 minutes. Obviously, if the machine must be stopped and lubricated manually every ten minutes, this would result in tremendous downtime and loss of productivity.
To address these needs, various automatic systems have been developed to provide lubrication during machine operation. Generally, such lubrication systems include a reservoir for lubricating material, a pump, supply lines, and one or more injectors arranged to deliver lubricant through feed lines to each of the lubrication points.
For example, a known automatic lubrication system is shown in FIG. 1. This system 1 includes a tank 2 which is fluidly connected to a pump 4 driven by a hydraulic motor 6. Lubricant is driven by the pump 4 through a supply line 8 to a number of downstream injector banks 10, each injector bank having two or more individual injectors 12 which supply lubricant through feed lines 14 to the areas in need of lubrication.
The hydraulic motor 6 is primarily controlled by a solenoid valve 22, which also controls a vent valve 16 disposed in the supply line 8 adjacent to the pump 4. The solenoid valve 22 is actuated automatically through a controller 24, but may also be manually actuated by an operator through controls typically located in the operator's cab.
In many applications, such as those that employ pressure-actuated injectors, it is necessary to control operation of the pump to achieve specific pressures at various points in the supply line. Such injectors, for example, are sold by Lincoln Industrial Corporation under the designation Series SL-1. These injectors have the benefit of supplying a metered quantity of lubricating fluid to the lubrication point with which the injector is associated, and are adjustable in that regard. However, these injectors are only fully actuated when pressure in the supply line at the injector reaches a specific level, after which the pressure in the supply line must be relieved to reset the injector.
To achieve the necessary pressure for firing the injectors, the controller 24 may operate based on a timer, causing the pump to operate for a duration that is expected to allow the necessary pressure to be reached at all of the injectors. That is, the controller is adapted to actuate the motor, pump and/or valve mechanisms to supply lubricant for a set duration, e.g. 120 seconds, every 10 minutes. For more precise control, known systems have included a downstream pressure sensor 26 in communication with the controller 24, and in connection with a timer, to provide a better estimation of the pressure at the injectors. For example, the pressure at a downstream location is monitored, and when a desired pressure is obtained at the sensor position, the controller adds, for example, 10 seconds, after which it is assumed that the necessary pressure has been obtained at the injectors, and, therefore, that the injectors have fully fired.
In the optimal situation, the pressure sensor would be placed directly at the location of the injector. However, due to the typically harsh environments in which the machines employing these systems tend to operate and other design considerations, it has typically proven impractical to place a pressure sensor far enough downstream to obtain the most accurate reading. For example, on a wheel loader or hydraulic excavator, placing a pressure sensor on the linkage or boom assembly, particularly near the bucket or other work implement, simply is not a viable option due to damage that will inevitably occur to the sensor.
As a result, the pressure sensors of known systems are typically placed far from the location of the furthest injectors, with a delay built into the controls to estimate when the downstream pressure has been achieved. For example, in the prior art system 1 just described, pressure sensor 26 is located on the vehicle frame, while the furthest injectors are located on the machine linkage assembly.
While better than a pure timer mechanism, known systems employing a single pressure sensor are still prone to inaccuracy. In particular, this occurs when the viscosity of the lubricant has been increased. This typically occurs, for example, when operating in low temperature conditions, or, more often, as the result of operators or maintenance personnel using an improper lubricant. In either case, the single sensor system may indicate a successful cycle where the downstream pressure has not actually been achieved. Thus, the system fails to lubricate the necessary components, causing premature failure and potential damage to the machine.
Another problem associated with conventional lubrication systems occurs when the pump pressure exceeds a maximum operating pressure. A pressure regulator is typically provided to ensure that the pump pressure does not exceed a threshold level. However, the pressure regulator may fail due to either improper adjustment or malfunctions. Excessive pressure may be caused, for example, by variation in the hydraulic supply pressure and flow to the hydraulic motor, as well as with variation in the performance of a pressure reducing valve between the hydraulic supply and the hydraulic motor. Moreover, the overall pump efficiency as a function of lubricant type, operating temperature, and wear or break-in may not be taken into account by a system relying on a pressure regulator alone.
It is therefore desirable to provide a better system for controlling such lubrication systems, and, in particular, a more precise method of determining the pressure at the injectors for improved efficiency and performance. The present disclosure is directed to overcoming one or more of the problems set forth above.